Combustion process



United COMBUSTION PaocEss i No Drawing. Application February 25, 1957Serial No. 641,874

6 Claims. (Cl. 158--117.5)

The present invention relates to the operation of furnaces in whichfluid fuels are burned. More particularly, it is concerned with a methodof improving and controlling the radiant heat or emissivity of flamesproduced in furnaces. i

In many types of furnaces wherein the fuel burned is oil, gas, ormixtures thereof, at least a part of the heat released by the flame istransferred from the flame to the body being heated by means ofradiation. This either occurs directly, as in the case of a solidcharge, or indirectly, as in the case of a liquid charge. Open hearthsteel furnaces, lime and cement kilns, annealing furnaces, tube stillheaters, cracking furnaces, and the likeare examples of many types offurnaces largely dependent upon radiant heat transfer. The presentinvention is especially directed to the operation of open hearthfurnaces in steel making processes, but the principles and process applyto these other types of furnaces as Well.

In all of such types of furnaces, the proportion of heat transferred tothe charge by radiation is largely fixed by the design of the furnaceand by the characteristics of the flame. For example, in an open hearthfurnace nearly all of the heat is transferred to the charge byradiation.- In the usual case of a tube still heater or kiln to which.

the charge is continuously fed at a constant temperature and rate, theproportion of radiant heat transfer depends upon the ratio of the tubesurface area which the flame seesT to the tube surface area which is incontact with the combustion gases, but which the flame cannot see. Aslong as outlet temperatures must remain constant at Industrial furnacesare ordinarily extremely large capi t'al investments and it is obviousthat increased flexibiiity in the, operation of such furnaces would behighly advantageous.

The addition of foreign bodies to fuel oils for the purpose ofincreasing emissivity of the flames during burning or combustion issuccessful but entailsa number of serious disadvantages. One of thesecomprises'the relaatent ice 1000 are maintained in true' solution by thelower molecular weight aromatics and heteroaromatics in the sys--. tern,the fuel oil will be optically clear when examinednaces. It is a moreparticular object of this invention to provide increased flexibility in'theradiation effects of flames burning in furnaces. It is a furtherobject of the invention to improve the economic aspects ofoperating suchfurnaces. Other objects will appear hereinafter. u

Now, in accordance with the presentinvention, it has been found that theradiation or emissivity (in the infrared spectral region) of a flamebeing burned in a furnace may be increased by precipitation of asubstantial proportion of the components having molecular weights; aboveabout 1000 (preferably 1000-5000) present in a residual fuel oil toyield agglomerates greater than cola loidal size and thereafter burningthe fuel oil containing; said particles, whereby flames of increasedemissivity are;

obtained. 7 Residual fuel oils generally consist of ablend of vacuumflashed or. thermally cracked residue in a mixture of;- lighterdistillates (cutter stock) of relatively lowviscosity. When the aromaticor heteroaromatic componentsofthe residue having molecularweightsgreater than about in thin layers. When the solubilizing power of thelower molecular weight components of the fuel oil is not sufficient tomaintain true solution, the occurrence'of molecular association betweenvarious of the higher molecular weight polar components leads to theformation of loose aggregates of molecules .into clusters whicheventually grow into aggregatessutliciently large to be visible to theunaided eye as a precipitate. This imperfeet, 'solubilization of thehigh molecular weight compo-1 nents maybe brought about by theaddition'of paraflinic components to the system. a

In accordance with a preferred version of the present invention, theprecipitated particles (including agglomerates or originally discreteparticles) are distributed in particle size over a range from about 0.5micron to about l microns, so that as the relatively smaller particlesare consumed and disappear from the flame, the relatively largerparticles still persist in acting as radiating tively high expense ofsuitable forms of carbon such as v i carbon black or acetylene black.The benefits of the reduction in the time necessary to heat a batch ofsteel ination into ichain like structures, thus reducing their emis-.sivity which is at a maximum when the particle is either spheroidal orsphericalshape. v

,;'It' is an "object? of the present invention to provide a method ercontrolling the radiation effects within furbodies. In accordance withone phase of the present invention, this range in particle size of theprecipitated par ticles may be effected by a differential timeofparticle size existence between several portions of the residual fuelbeing introduced into the furnace. If, for example, 1

the smallest particles are formed by a residence time outside ,of thefurnace and prior to burning of'about 5 seconds, or less, then it ispreferred that an appreciable portion of the fuel oil be subjected toprecipitation tech Y niques; for a time prior entrance into the furnaceof at" least about 30 seconds or more, so that the necessary time forparticle growth is gained after which both particle-containing residualfuel streams are introduced, either together or separately, into theflame-burning area.

1 Since it is preferred that substantially continuous ele' vatedemissivity throughout the entire area of the flame is obtained, it ispreferred that at least about 10% by weight of the precipitatedparticles have diameters lessthan about 0.5 microns and at least 10% byweight of the particles have diameters greater than about 10-micronsQ-"Thus, t ere is .virtual insurance that the flame, wlll contain at alltimes an emissiori improving portion of-radiatingparticles, even thoughthe flame be of, a

length from about several inches to as. much as. 35 feet. Flames fromabout 15 to 30 feet are commonly emlayed in such large scale industrialinstallationsas open hearthsteel furnaces and the like. The upper,

limit of particle size is determined as that .sizeparticle which willjust I be consumed [in the particular -flam e whose length, temperature,percent excess air' and linear Patented Nov.,17, 9

velocity are known. For any given flame and a knowl edge of the furnacegeometry this maximum particle size can be determined.

,Thejueloils to be treated in accordance with the present" invention aredefined as being asphaltogenic in nature, by which is meant that saidfuel oils are normally residual fuels or contain substantial quantitiesof residual petroleum components,-said residual components comprising inpart those bodies of reduced solubility characteristi'cs which havemolecular weights above about 1000, usually 1000-5000.

A further improvement in the present invention, especially as applied tosituations such as existin open hearth 'steel making furnaces, comprisesmaintaining the flame profile substantially constant during the entiresteel making process, and varying the'radiation of the flame bycontrolling the proportion of suitabl'eparticles in the fuel stream. Astill further improvement in this respect comprises maintaining thetotal fuel input substantially constant throughout the steel makingprocess, thus maintaining the flame profile substantially unalteredduring the same period, but varying the radiation characteristicsthereof by variation in particle proportion.

The open hearth furnace is a batch furnace. Steel scrap, pig iron, andsometimes a small proportion of ore are "charged to the furnace, meltedand refined. In the first stage of the melt, the charging period, thesolids are cold and present an irregular surface to the flame andcombustion gases. The actual charge to the furnace is normally carriedout in a series of steps'since the unmelted mass usually is too largefor the entire charge to be made at one time. Consequently,substantially half of the charge is inserted in the furnace andpartially or fully melted before further portions of the charge areadded. Upon commencement ofheating-lat least a portion of the chargemelts sufliciently to substantially submerge the remaining solids and:the surface of the charge becomes flat. \Vhen this stagehas beenreached, the so-called melting period begins. When the ingredients haveall reached the melt stage -(or substantially so), the refining periodstarts, during'which the liquid charge is maintained at a high andsubstantially constant temperature for the necessary time to completepurification by separation of the slag-fromthe' main body of the meltedsteel.

It is economically desirable to minimize the time consumed during thecharging and melting periods in order to maintain a high rate ofproduction of steel fro'mthe furnace. During these first two periods(charging and melting) the temperature is being raised continually and,consequently, during this time the-maximum degree of radiation from theflame is desirable. The maximum fuel input rate is limited by themelting temperature of the roof of the furnace as well as theoptimum'flame profile for efiicient transfer of heat from the flame tothe melting charge. During the charging period high fuel inputrates maybe employed when both the'charge and'the furnace refractory roof arerelatively cool.

However,- during the melting period, the fuel input rateis limited bythe maximum allowable temperature of the refractory roof which isordinarily in the order of- 2800- 3000" F. Since the temperature of thecharge during this period gradually rises from 2400 to 2600 F., there isa very small margin between required and maximum allowable furnacetemperatures.

'While the fuel input rate can be-varied, it will be obvious that theflame profile will alter radically with any change made in this inputrate. Hence, it is desirable to establish the optimum flame profile fora given rate of fuel input and thereafter maintain the same rateof'total fuel consumption. The present processis based upon theseconsiderations and provides the flexibility necessary for successfuloperation thereof. 7 Fuels have been modified in the past by theincorporat nun of s'olidfuel materials, especially powdered coal:

However, the use of powdered coal in fuel oil suspension does notprovide the desired increase in radiant heat, since the powdered coalparticles are either relatively extremely coarse and consequently do notpresent the surface area necessary for optimum black body radiation, or(due to burning rates slower than that of oil) must be ground much finerthan precipitated oil particles if they are to be completely consumed.Other solid fuel components used as proposed heretofore, have beenincorporated in the entire body of the fuel oil and consequentlypermitted no latitude in the alteration of the radiation of the flamewhich must necessarily have remained at a constant value for any totalrate of fuel input. Moreover, the principal disadvantage which wasexperienced with these prior art coal and carbon black suspensionscomprised the difficulty of maintenance of the suspension, since in therelatively dilute form in which they are normally employed the particlesare not self-supporting and tend to settle out. This property may beovercome in part by incorporattion of certain suspending agents andsurfactants, but this is an uneco nomical means of creating andmaintaining the suspen sions and also entails certain problems such asthe creation of undesirable ash. Since the fuel input into a largefurnace such as an open hearth furnace is extremely high, the ashproblem becomes serious due to deposition thereof on the sides of thefurnace and the operating parts thereof.

The improvement caused by this invention is appar ently based upon theincreased emission of radiant gas oil bottoms 'as well as thermally andcatalytically cracked reforming bottoms. The precipitation index isdefined as the percentage of alpha-methyl naphthalene in a mixture withcetane which will just dissolve the least soluble component of theresidue: the higher the precipitation index the more insoluble theresidue.

The particles are precipitated in an amount between about 1 and about10% by weight, based on the total fuel. .This is preferably effected byaddition to the asphaltogenic residual fuel oil ofa precipitating liquidhaving a low solvency index, the latter term being defined as follows:The solvency index of a liquid is defined as the volume percentage ofalpha-methyl naphthalene in an alpha-methyl naphthalene-cetane mixtureequivalent in solvency to that of the liquid under exam-' matron; Forthe most part, low solvency precipitating liquids include parafiinichydrocarbons having from 3 to 20 (P eferably 5-20) carbon atoms permolecule, the

most practical one of which is an extracted kerosene fraction, sincethis product contains a high concentration of the higher normal alkaneswhich are still liquid at ambient temperature. These higher normalalkanes, preferably having molecular weights between 150 and 250, aremore effective precipitants than the lower alkanes.

Following are typical solvency indices for specific conipounds:

Compound: Solvency index Alpha-methyl naphthalene Toluene V 77Cyclohexane 47 l-octene 20.8 l-dodecene 19.0 n-Hexane 1 8 .2 n-O'ctane16.7 n-Dodecane 10 .3 'n-Tetradecene 7.4

dither precipitating liquids include normally gaseous hydrocarbons, suchas propane and butane, as well as the normally liquid hydrocarbons, suchas hexane or decane. a The proportion of precipitating liquid to beadded to the residual fuel oil will depend upon a number of factors,including the solvency index of the precipitating liquid, theprecipitation index of the fuel oil, the proportion of particlesdesired, and the average diameter of the particles-required, in additionto the lapse of time between mixing of the precipitant with the fuel oiland the time of combustion. Normally, however, it will be found thatprecipitants having from 3 to 20 carbon atoms per molecule and having asolvency index betweenabout 0 and about 50 when added to the preferredtype ofresidual fuel oils having precipitation index between about 20and about 80 are utilized in amounts fromxabout 20% to about 80% byweight, based on the fuel'oil, and ordinarily then constitutenot only aprecipitating agent but also a combustible component of the fuel oilcomposition.

It has been ascertained that non-aromatic (aliphatic and/ orcycloaliphatic) precipitating agents such as kero sene and the like,actually exhibit a lower emissivity than theordinary residual fuel oil.However, when the me cipitating agent and the fuel oil are combined insuch proportions as to precipitate particles as described above,the-emissivity (in the infra red region) of the burning fuel compositionis substantially higher than that experienced by either the fuel oilalone or by the precipi tating agent alone. Y Y

The effect of increasing the emissivity of the combusting fuels is ofgreat economic significance since it has been ascertained that theaverage time of completing a run in a standard commercial open hearthfurnace can be reduced as much as about 10%.

- The addition of the precipitating liquid to the residual fuel oil ispreferably effected just prior to injection into the furnace andcombustion of the fuel composition. The timing will be adjusted toproduce the optimum size of particles in accordance with the limitationsset forth hereinbefore but normally will be between about 1 second and24 hours and preferably between about 30 seconds and /z"hour. .Theproductionof particles in a residual fuel, according to the presentprocess, results in sub stantially spherical particles which, upon agingin the fuel oil composition, tend to agglomerate into larger bodieswhich still maintain their essentially spherical shape. This is sharplydifferentiated from the chain-like agglomerates which are created uponthe aging of carbon black particles suspended in fuel oils.

In order to, maintain a substantially constant supply of radiatingprecipitated bodies throughout the entire length of a fuel flame such asin an open hearth furnace, it is preferred that the particle sizedistribution be spread between the limits already stated, namely,between about 0.5 micron and about 150 microns. ficult to attain if theprecipitating agent is added to the fuel oil at only one particular timeprior to combustion of the fuel oil composition. Therefore, inaccordance with one phase of this invention, it is a preferred processto inject portions of the precipitating agent into fuel oil being fed toa burner at two or more time units prior to burning so that an elapsedtime is permitted for part of, the particles to agglomerate or grow andform the relatively coarser-varieties which have a more extended lifeprior to being completely burnt in the flame during combustion. Thismultiple addition of a precipitating liquid added thereto so as toenable the growth or agglomeration of particles to occur; The two ormore portions of the fuel may be combined at the burner or may beinjected into the combustlon area through separate nozzles.

This may be diftion of the fuel oil in which the relatively largerparticles 6 the necessary extendedparticle formation period prior' toburning. Y

By utilization of the present process of precipitating fuel componentsin the fuel stream of such furnaces, it has been found that greateconomic advantages can be obtained, for example, in the cycle time forthe production of-steel. By the precipitation of 1.5-5% insolubleparticles into the fuel oil utilized for the heating of an open hearthfurnace, for. example, during the charging and melting stagesbut'omitted during the refining stage, a 10% reduction in total cycletime can be effected. -By maintaining the total fuel input constantduring the entire period of steel production (or during any othercomparable process, such as cement production) the-flame profile wassubstantially unalteredfb'ut the radiation thereof was radically changedby the injection or omission of the colloidal particles. The increasedflame luminosity did not appear to affect refractory life in suchfurnaces since the temperature of the flame was not substantiallydifierent from that of the flame without particle formation. Thefollowing examples illustrate the process of thepresent invention.

Example I A fuel composition was prepared by the addition of 40 parts byweight ofan extracted kerosene (having a'solvency'index of about 30) to60 par-ts by weight of two fuel oils having the following properties: r

Fuel .Oil A Fuel Oil B Unblended thermal residue, percent 57 I 89.0 Lubeoil extract, percent 18 0 Thermally cracked pressure distillate,percent. 25 11.0 Gravity, API 12. 2 8.5 Flash, Pensk -Martin, F; 218-194 Viscosity, SS at 122 F. 27. 5' 164 Four point, 9 l -10 +25 Sulfur,percent 0. 93 0. 89 Precipitation index 48 "48 When'these'combinationsof kerosene and fuel oils were burned after a pafticle formation periodof 1-10 minutes and; the flame examined for radiation by means of aninfrared spectrometer, it was found that the combustion oftheccompositions containing the resulting precipitated particles gave asubstantially greater intensity in a useful radiation range (L-3.5:microns) than are produced by combustion of the unmodified fuel oils.

The same was true after the composition containing the precipitatingliquid .and the vresulting par ticles was al-' lowed to age for 24hours.

The deleanu extracted kerosene employed in this test had the followingproperties:

Gravity, APT 42.5 Solvency index 30 Aromatics, percent 3.;7' Boilingrange, F 384-49 Flash point, Pensky-Martin, F 155 (approximately by 10%)are necessary for reaching the correct stage of charging and melting ofthe steel charge when precipitated fuel particles are present :inthefuel oil composition than when the unmodified fuel oils are are to beformed into a storage tank preferably containing agitation means orthrough-a coil designed to increase the residence time of the fuel oiltherein so as to provide apt-i042? 7 fuel precipitated in the form ofparticles. The table summarizes the results obtained:

I claim as my invention:

1. A method of improving the radiation emission of an asphaltogenicresidual fuel oil having a precipitation index of at least 40 during thecombustion thereof which comprises precipitating therein between about1% and about by weight, based on total fuel components, of highmolecular weight fuel components as substantially spherical particles byadmixing -80% by weight based on the fuel oil, of aliphatic hydrocarbonshaving 3-20 carbon atoms per molecule therewith and thereafter burningthe particle-containing fuel, whereby its emission of radiant energy inthe infra red range is increased, said admixing being effected from 30seconds to one-half hour prior to combustion.

2. A method of improving the radiation emission: of an asphaltogenicresidual fuel oil having a precipitation index of at least- 40 duringthe combustion thereof which comprisesf precipitating therein betweenabout 1% and about 10% by weight, based on total fuel components ofinsoluble fuel substantially spherical particles by ad mixing 20-80% byweight, based on' the fuel oil, of substantially aliphatic C -Chydrocarbons therewith and thereafter burning the particle-containingfuel, whereby its emission of radiant energy in the infra red range isincreased, said admixing being effected from 30 seconds toone-half hourprior to combustion. W

3. A method of improving the radiation emission of an asphaltogenicresidual fuel oil having a precipitation index of atleast 40 during thecombustion thereof which comprises precipitating therein between about1% and about 10% by weight, based on' total fuel components, of,insoluble fue'l components substantially spherical particles havingdiameters between 0.5 microns and 150 microns by admixing 20-80% byweight, based on the fuel oil, of non-aromatic hydrocarbons boiling inthe kerosene range and thereafter burning the particle-containing fuel,whereby its emission of radiant energy in the infrared range isincreased, said admixing being effected flO'Ih'30 seconds to one-halfhour prior to combustion.

4. A methodof improving the radiation emission of an asphaltogenic'residual fuel oil having a precipitation-indexof at least 40 during thecombustion thereof which comprises precipitating therein between about1% and about 10% by weight, based on total fuel components; of fuelcomponent substantially spherical particles of substantially sphericalshape, at least by weight of which have diameters between about 0.5micron and microns and thereafter burning the particle-containing fuel,whereby its emission of radiant energy in the infra red range isincreased, said precipitating being effected by'a'd-' dition to the fueloil of 20-80% by weight based on the fuel oil of hydrocarbons having3-20 carbon atoms per molecule at a time between about 1 second and 24hours prior to combustion.

5. A method'of improving the radiation emissionof an asphaltogenicfueloil having a precipitation index of 25- 80 during the combustion thereofwhich comprises adding thereto, at a time between 1 second and 24 hoursprior to combustion, 20-80% by Weight, based on the fuel oil, ofaliphatic hydrocarbons having 3-20 carbon atoms per molecule, wherebyl-l0% by weight, based on the oil plus hydrocarbons, of componentshaving molecular weights above about 1000 are precipitated assubstantially spherical particles and thereafter burning the resultingmixture, the incandescent particles increasing emission of radiantenergy in the infra-red range during burning.

6 A method of improving the radiation emission of an asphaltogenic fueloil having'a precipitation index of at least 25 during the combustionthereof which comprises adding thereto, at a time between 1 second and24 hours prior to combustion, 20-80% by weight, based on fuel oil", ofaliphatic hydrocarbons haiving 3-20 carbon atoms per molecule, wherebyl-l0% by weight, based on the oil plus hydrocarbons, of componentshaving molecular weights above about 1000 are precipitated assubstantially spherical particles and thereafter burning the resultingmixture, the incandescent particles increasing emission of radiantenergy in the infra-red'range during burning.

References Cited in the file of this patent UNITED STATES PATENTSChilton Feb. 5, 1957'

1. A METHOD OF IMPROVING THE RADIATION EMMISSION OF AN ASPHALTOGENICRESIDUAL FUEL OIL HAVING A PRECIPITATION INDEX OF AT LEAST 40 DURING THECOMBUSTION THEREOF WHICH COMPRISES PRECIPITATING THEREIN BETWEEN ABOUT1% AND ABOUT 10% BY WEIGHT, BASED ON TOTAL FUEL COMPONENTS, OF HIGHMOLECULAR WEIGHT FUEL COMPONENTS AS SUBSTANTIALLY SPHERICAL PARTICLES BYADMIXING 20-80% BY WEIGHT BASED ON THE FUEL OIL, OF ALIPHATICHYDROCARBONS HAVING 3-20 CARBON ATOMS PER MOLECULE THEREWITH ANDTHEREAFTER BURNING THE PARTICLE-CONTAINING FUEL, WHREBY ITS EMISSION OFRADIANT ENERGY IN THE INFRA RED RANGE IS INCREASED, SIAD ADMIXING BEINGEFFECTED FROM 30 SECONDS TO ONE-HALF HOUR PRIOR TO COMBUSTION.